Wearable exoskeletons have been designed for medical, commercial and military applications. Medical exoskeletons are designed to help restore a user's mobility. Commercial and military exoskeletons help prevent injury and augment a user's stamina and strength by alleviating loads supported by workers or soldiers during strenuous activities. Exoskeletons designed for use by able-bodied users often act to improve the user's stamina by transferring the weight of a tool or load through the exoskeleton structure and to the ground, thus decreasing the weight borne by the user. For the exoskeleton to transfer this weight to the ground, each exoskeleton support member and exoskeleton joint between the exoskeleton weight and the ground must be able to act as a conduit of this force around the user. This requires a degree of rigidity, seen in the joints of current exoskeletons, that can limit the range of motion of some exoskeleton joints. By limiting the flexibility at these joints, the mobility and maneuverability of the exoskeleton is reduced, thereby limiting the usefulness of the exoskeleton in certain applications. This is an issue in both passive weight-bearing exoskeletons and powered exoskeletons. In the case of powered exoskeletons, the weight of actuators and power systems such as batteries must also be borne by the structure and joints of the exoskeleton.
Current exoskeleton designs rely on inflexible compression members to support the weight of the exoskeleton structure, with the exoskeleton joints being comprised of rotating or pivoting components that connect two rigid members at a fixed distance (the distance being the joint itself) and bear weight through compression. This greatly limits the degrees of freedom of one rigid exoskeleton member relative to the adjoining exoskeleton member. While some exoskeleton joints, such as the knee, require rotation only in a single plane with a fixed distance between the connected rigid members, other joints, such as the hip and ankle, are better served by rotation in two or more planes as well as translation. As one example of the consequences of the limited range of motion of exoskeleton joints, current exoskeleton ankles are incapable of any significant eversion or inversion motion. As a result, the bottom of an exoskeleton foot cannot compensate for a slope in the coronal plane, making current exoskeletons incapable of walking on many types of terrain. As another example, the inability (or reduced ability) of exoskeleton ankle and hip joints to rotate in the transverse plane makes turning a walking or standing exoskeleton difficult. With respect to the hip joint specifically, while the human hip is a ball and socket joint that does not require translation, an exoskeleton hip joint must pass around the human hip. As an exoskeleton hip cannot be collocated with the center of human hip joint rotation, translation about an exoskeleton hip joint allows for greatly improved flexibility for the exoskeleton wearer at the hip—particularly in movements such as medial and lateral rotation or combinations of rotation with adduction, abduction, extension, or flexion. Such improved flexibility would be a great advantage to exoskeletons being worn in highly dynamic environments, such as those seen in athletic activities or combat scenarios.
Due to the limitations imposed on exoskeleton use by the restricted range of motion in exoskeleton joints, there exists a need in the art to develop a device that allows improved flexibility in weight-bearing exoskeleton joints. There also exists a need in the art to develop such a device that is low weight.